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The lewis structure of trinitramide has four major resonance structures, whereby the lone pairs of the central nitrogen can resonate with the nitro groups.

This seems to indicate that each of the nitrogen atoms would be sp2 hybridized, and the entire molecule would be planar. In fact, the Wikipedia ball-and-stick image for trinitramide seems to indicate it so.

enter image description here

However, based on quantum mechanical calculations, trinitramide is in fact non-planar. Why is this so? What drives its non-planarity?

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    $\begingroup$ Steric hindrance, maybe? $\endgroup$ – Oscar Lanzi Jun 18 at 23:01
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    $\begingroup$ I would assume it’s a combination of steric and charge repulsion between the oxygen atoms. The experimentally determined structure in doi.org/10.1002/anie.201007047 shows the nitro groups essentially at right angles to each other. $\endgroup$ – Andrew Jun 18 at 23:12
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    $\begingroup$ I have extensively written about the isoelectronic trinitromethanide anion: chemistry.stackexchange.com/q/32354/4945 $\endgroup$ – Martin - マーチン Jun 18 at 23:14
  • $\begingroup$ Doesn't the paper you have linked tell more than what we can presumably say? Interestingly, they not only say isn't planar, but pyramidal. There should be a comment atop the calculations. Otherwise take it at the level of their work. Perhaps one could calculate a different situati $\endgroup$ – Alchimista Jun 19 at 12:42

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